Preparation of nanocrystallites

ABSTRACT

A method of manufacturing a nanocrystallite from a M-containing salt forms a nanocrystallite. The nanocrystallite can be a member of a population of nanocrystallites having a narrow size distribution and can include one or more semiconductor materials. Semiconducting nanocrystallites can photoluminesce and can have high emission quantum efficiencies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. application Ser. No. 10/455,629, filed on Jun. 6, 2003, which is acontinuation of U.S. application Ser. No. 09/732,013, filed on Dec. 8,2000, now U.S. Pat. No. 6,576,291, each of which is incorporated byreference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract No.DMR-98-08941 from the National Science Foundation. The government mayhave certain rights in the invention.

TECHNICAL FIELD

The invention relates to methods of manufacturing a nanocrystallite.

BACKGROUND

Nanocrystallites having small diameters can have properties intermediatebetween molecular and bulk forms of matter. For example,nanocrystallites based on semiconductor materials having small diameterscan exhibit quantum confinement of both the electron and hole in allthree dimensions, which leads to an increase in the effective band gapof the material with decreasing crystallite size. Consequently, both theoptical absorption and emission of nanocrystallites shift to the blue(i.e., to higher energies) as the size of the crystallites decreases.

Methods of preparing monodisperse semiconductor nanocrystallites includepyrolysis of organometallic reagents, such as dimethyl cadmium, injectedinto a hot, coordinating solvent. This permits discrete nucleation andresults in the controlled growth of macroscopic quantities ofnanocrystallites. Organometallic reagents can be expensive, dangerousand difficult to handle.

SUMMARY

The invention features methods of manufacturing a nanocrystallite. Thenanocrystallite has a diameter of less than 150 Å. The nanocrystallitecan be a member of a population of nanocrystallites having a narrow sizedistribution. The nanocrystallite can be a sphere, rod, disk, or othershape. The nanocrystallite can include a core of a semiconductormaterial. The core can have an overcoating on a surface of the core. Theovercoating can be a semiconductor material having a compositiondifferent from the composition of the core. Semiconductingnanocrystallites can photoluminesce and can have high emission quantumefficiencies. The method forms the nanocrystallite from an M-containingsalt. The nanocrystallite can include a core having the formula MX,where M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium,thallium, or mixtures thereof, and X is oxygen, sulfur, selenium,tellurium, nitrogen, phosphorus, arsenic, antimony, or mixtures thereof.The M-containing salt can be the source of M in the nanocrystallite. AnX-containing compound can be the source of the X in the nanocrystallite.

The M-containing salt can be a safe, inexpensive starting material formanufacturing a nanocrystallite relative to typical organometallicreagents which can be air sensitive, pyrophoric, or volatile. TheM-containing salt is not air sensitive, is not pyrophoric, and is notvolatile relative to organometallic reagents.

In one aspect, the invention features a method of manufacturing ananocrystallite. The method includes contacting a metal, M, or anM-containing salt, and a reducing agent to form an M-containingprecursor, M being Cd, Zn, Mg, Hg, Al, Ga, In or Tl. The M-containingprecursor is contacted with an X donor, X being O, S, Se, Te, N, P, As,or Sb. The mixture is then heated in the presence of an amine to formthe nanocrystallite. In certain embodiments, heating can take place inthe presence of a coordinating solvent.

In another aspect, the invention features a method of manufacturing ananocrystallite including contacting a metal, M, or an M-containingsalt, and a reducing agent to form an M-containing precursor, contactingthe M-containing precursor with an X donor, and heating the mixture toform the nanocrystallite. In certain embodiments, heating can take placein the presence of a coordinating solvent.

In another aspect, the invention features a method of manufacturing ananocrystallite including contacting a metal, M, or an M-containingsalt, an amine, and an X donor, and heating the mixture to form thenanocrystallite.

In yet another aspect, the invention features a method of overcoating acore nanocrystallite. The method includes contacting a corenanocrystallite population with an M-containing salt, an X donor, and anamine, and forming an overcoating having the formula MX on a surface ofthe core. In certain embodiments, a coordinating solvent can be present.

The amine can be a primary amine, for example, a C₈-C₂₀ alkyl amine. Thereducing agent can be a mild reducing agent capable of reducing the M ofthe M-containing salt. Suitable reducing agents include a 1,2-diol or analdehyde. The 1,2-diol can be a C₆-C₂₀ alkyl diol. The aldehyde can be aC₆-C₂₀ aldehyde.

The M-containing salt can include a halide, carboxylate, carbonate,hydroxide, or diketonate. The X donor can include a phosphinechalcogenide, a bis(silyl)chalcogenide, dioxygen, an ammonium salt, or atris(silyl)pnictide.

The nanocrystallite can photoluminesce with a quantum efficiency of atleast 10%, preferably at least 20%, and more preferably at least 40%.The nanocrystallite can have a particle size (e.g., average diameterwhen the nanocrystallite is spheroidal) in the range of about 20 Å toabout 125 Å. The nanocrystallite can be a member of a substantiallymonodisperse core population. The population can emit light in aspectral range of no greater than about 75 nm at full width at half max(FWHM), preferably 60 nm FWHM, more preferably 40 nm FWHM, and mostpreferably 30 nm FWHM. The population can exhibit less than a 15% rmsdeviation in diameter of the nanocrystallites, preferably less than 10%,more preferably less than 5%.

The method can include monitoring the size distribution of a populationincluding of the nanocrystallite, lowering the temperature of themixture in response to a spreading of the size distribution, orincreasing the temperature of the mixture in response to when monitoringindicates growth appears to stop. The method can also include exposingthe nanocrystallite to a compound having affinity for a surface of thenanocrystallite.

The method can include forming an overcoating of a semiconductormaterial on a surface of the nanocrystallite. The semiconductor materialcan be a group II-VI, III-V or IV semiconductor, such as, for example,ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO,HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP,InAs, InSb, TlN, TIP, TlAs, TlSb, or mixtures thereof.

The details of one or more embodiments of the invention are set forth inthe description below. Other features, objects, and advantages of theinvention will be apparent from the description and from the claims.

DETAILED DESCRIPTION

The method of manufacturing a nanocrystallite is a colloidal growthprocess. Colloidal growth occurs by rapidly injecting an M-containingsalt and an X donor into a hot coordinating solvent including an amine.The injection produces a nucleus that can be grown in a controlledmanner to form a nanocrystallite. The reaction mixture can be gentlyheated to grow and anneal the nanocrystallite. Both the average size andthe size distribution of the nanocrystallites in a sample are dependenton the growth temperature. The growth temperature necessary to maintainsteady growth increases with increasing average crystal size. Thenanocrystallite is a member of a population of nanocrystallites. As aresult of the discrete nucleation and controlled growth, the populationof nanocrystallites obtained has a narrow, monodisperse distribution ofdiameters. The monodisperse distribution of diameters can also bereferred to as a size. The process of controlled growth and annealing ofthe nanocrystallites in the coordinating solvent that follows nucleationcan also result in uniform surface derivatization and regular corestructures. As the size distribution sharpens, the temperature can beraised to maintain steady growth. By adding more M-containing salt or Xdonor, the growth period can be shortened.

The M-containing salt is a non-organometallic compound, e.g., a compoundfree of metal-carbon bonds. M is cadmium, zinc, magnesium, mercury,aluminum, gallium, indium or thallium. The M-containing salt can be ametal halide, metal carboxylate, metal carbonate, metal hydroxide, ormetal diketonate, such as a metal acetylacetonate. The M-containing saltis less expensive and safer to use than organometallic compounds, suchas metal alkyls. For example, the M-containing salts are stable in air,whereas metal alkyls a generally unstable in air. M-containing saltssuch as 2,4-pentanedionate (i.e., acetylacetonate (acac)), halide,carboxylate, hydroxide, or carbonate salts are stable in air and allownanocrystallites to be manufactured under less rigorous conditions thancorresponding metal alkyls.

Suitable M-containing salts include cadmium acetylacetonate, cadmiumiodide, cadmium bromide, cadmium hydroxide, cadmium carbonate, cadmiumacetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinchydroxide, zinc carbonate, zinc acetate, magnesium acetylacetonate,magnesium iodide, magnesium bromide, magnesium hydroxide, magnesiumcarbonate, magnesium acetate, mercury acetylacetonate, mercury iodide,mercury bromide, mercury hydroxide, mercury carbonate, mercury acetate,aluminum acetylacetonate, aluminum iodide, aluminum bromide, aluminumhydroxide, aluminum carbonate, aluminum acetate, galliumacetylacetonate, gallium iodide, gallium bromide, gallium hydroxide,gallium carbonate, gallium acetate, indium acetylacetonate, indiumiodide, indium bromide, indium hydroxide, indium carbonate, indiumacetate, thallium acetylacetonate, thallium iodide, thallium bromide,thallium hydroxide, thallium carbonate, or thallium acetate.

Alkyl is a branched or unbranched saturated hydrocarbon group of 1 to100 carbon atoms, preferably 1 to 30 carbon atoms, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl,tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, as well ascycloalkyl groups such as cyclopentyl, cyclohexyl and the like.Optionally, an alkyl can contain 1 to 6 linkages selected from the groupconsisting of —O—, —S—, -M- and —NR— where R is hydrogen, or C₁-C₈ alkylor lower alkenyl.

Prior to combining the M-containing salt with the X donor, theM-containing salt can be contacted with a coordinating solvent and a1,2-diol or an aldehyde to form an M-containing precursor. The 1,2-diolor aldehyde can facilitate reaction between the M-containing salt andthe X donor and improve the growth process and the quality of thenanocrystallite obtained in the process. The 1,2-diol or aldehyde can bea C₆-C₂₀ 1,2-diol or a C₆-C₂₀ aldehyde. A suitable 1,2-diol is1,2-hexadecanediol and a suitable aldehyde is dodecanal.

The X donor is a compound capable of reacting with the M-containing saltto form a material with the general formula MX. Typically, the X donoris a chalcogenide donor or a pnictide donor, such as a phosphinechalcogenide, a bis(silyl)chalcogenide, dioxygen, an ammonium salt, or atris(silyl)pnictide. Suitable X donors include dioxygen,bis(trimethylsilyl)selenide ((TMS)₂Se), trialkyl phosphine selenidessuch as (tri-n-octylphosphine)selenide (TOPSe) or(tri-n-butylphosphine)selenide (TBPSe), trialkyl phosphine telluridessuch as (tri-n-octylphosphine)telluride (TOPTe) orhexapropylphosphorustriamide telluride (HPPTTe),bis(trimethylsilyl)telluride ((TMS)₂Te), sulfur,bis(trimethylsilyl)sulfide ((TMS)₂S), a trialkyl phosphine sulfide suchas (tri-n-octylphosphine)sulfide (TOPS), tris(dimethylamino)arsine, anammonium salt such as an ammonium halide (e.g., NH₄Cl),tris(trimethylsilyl)phosphide ((TMS)₃P), tris(trimethylsilyl)arsenide((TMS)₃As), or tris(trimethylsilyl)antimonide ((TMS)₃Sb).

The coordinating solvent can help control the growth of thenanocrystallite. The coordinating solvent is a compound having a donorlone pair that, for example, has a lone electron pair available tocoordinate to a surface of the growing nanocrystallite. Solventcoordination can stabilize the growing nanocrystallite. Typicalcoordinating solvents include alkyl phosphines and alkyl phosphineoxides, however, other coordinating solvents, such as pyridines, furans,and amines may also be suitable for the nanocrystallite production.Examples of suitable coordinating solvents include tri-n-octyl phosphine(TOP) and tri-n-octyl phosphine oxide (TOPO). Technical grade TOPO canbe used.

The nanocrystallite manufactured from an M-containing salt grows in acontrolled manner when the coordinating solvent includes an amine.Preferably, the coordinating solvent is a mixture of the amine and analkyl phosphine oxide in a mole ratio of 10:90, more preferably 30:70and most preferably 50:50. The combined solvent can decrease sizedispersion and can improve photoluminescence quantum yield of thenanocrystallite.

The amine in the coordinating solvent contributes to the quality of thenanocrystallite obtained from the M-containing salt and X donor. Thepreferred amine is a primary alkyl amine, such as a C₂-C₂₀ alkyl amine,preferably a C₈-C₁₈ alkyl amine. One suitable amine for combining withtri-octylphosphine oxide (TOPO) is 1-hexadecylamine in a 50:50 moleratio. When the 1,2-diol or aldehyde and the amine are used incombination with the M-containing salt to form a population ofnanocrystallites, the photoluminescence quantum efficiency and thedistribution of nanocrystallite sizes are improved in comparison tonanocrystallites manufactured without the 1,2-diol or aldehyde or theamine.

Size distribution during the growth stage of the reaction can beestimated by monitoring the absorption line widths of the particles.Modification of the reaction temperature in response to changes in theabsorption spectrum of the particles allows the maintenance of a sharpparticle size distribution during growth. Reactants can be added to thenucleation solution during crystal growth to grow larger crystals. Bystopping growth at a particular nanocrystallite average diameter andchoosing the proper composition of the semiconducting material, theemission spectra of the nanocrystallites can be tuned continuously overthe wavelength range of 400 nm to 800 nm. The nanocrystallite has adiameter of less than 150 Å. A population of nanocrystallites hasaverage diameters in the range of 20 Å to 125 Å.

Nanocrystallites composed of semiconductor material can be illuminatedwith a light source at an absorption wavelength to cause an emissionoccurs at an emission wavelength, the emission having a frequency thatcorresponds to the band gap of the quantum confined semiconductormaterial. The band gap is a function of the size of the nanocrystallite.The narrow size distribution of a population of nanocrystallites canresult in emission of light in a narrow spectral range. Spectralemissions in a narrow range of no greater than about 75 nm, preferably60 nm, more preferably 40 nm, and most preferably 30 nm full width athalf max (FWHM) can be observed. The breadth of the photoluminescencedecreases as the dispersity of nanocrystallite diameters decreases.

The particle size distribution can be further refined by size selectiveprecipitation with a poor solvent for the nanocrystallites, such asmethanol/butanol as described in U.S. application Ser. No. 08/969,302,incorporated herein by reference. For example, nanocrystallites can bedispersed in a solution of 10% butanol in hexane. Methanol can be addeddropwise to this stirring solution until opalescence persists.Separation of supernatant and flocculate by centrifugation produces aprecipitate enriched with the largest crystallites in the sample. Thisprocedure can be repeated until no further sharpening of the opticalabsorption spectrum is noted. Size-selective precipitation can becarried out in a variety of solvent/nonsolvent pairs, includingpyridine/hexane and chloroform/methanol. The size-selectednanocrystallite population can have no more than a 15% RMS deviationfrom mean diameter, preferably 10% RMS deviation or less, and morepreferably 5% RMS deviation or less.

Transmission electron microscopy (TEM) can provide information about thesize, shape, and distribution of the nanocrystallite population. Powderx-ray diffraction (XRD) patterns can provided the most completeinformation regarding the type and quality of the crystal structure ofthe nanocrystallites. Estimates of size were also possible sinceparticle diameter is inversely related, via the X-ray coherence length,to the peak width. For example, the diameter of the nanocrystallite canbe measured directly by transmission electron microscopy or estimatedfrom x-ray diffraction data using, for example, the Scherrer equation.It also can be estimated from the UV/Vis absorption spectrum.

The method can also be used to overcoat a core semiconductor material.Overcoating can improve the emission quantum efficiency of the core.Semiconductor band offsets determine which potential shell materialsprovide energy barriers for both the electron and hole. For example,ZnS, ZnSe or CdS overcoatings can be grown on CdSe or CdTenanocrystallites. An overcoating process is described in U.S.application Ser. No. 08/969,302, incorporated herein by reference in itsentirety. The overcoating can be grown by the method includingcontacting a core with a mixture including an M-containing salt and theX donor in the presence of an amine. By adjusting the temperature of thereaction mixture during overcoating and monitoring the absorptionspectrum of the core, overcoated materials having high emission quantumefficiencies and narrow size distributions can be obtained.

The outer surface of the nanocrystallite includes an organic layerderived from the coordinating solvent used during the growth process.The surface can be modified by repeated exposure to an excess of acompeting coordinating group. For example, a dispersion of the cappednanocrystallite can be treated with a coordinating organic compound,such as pyridine, to produce crystallites which dispersed readily inpyridine, methanol, and aromatics but no longer dispersed in aliphaticsolvents. Such a surface exchange process can be carried out with anycompound capable of coordinating to or bonding with the outer surface ofthe nanocrystallite, including, for example, phosphines, thiols, aminesand phosphates. The nanocrystallite can be exposed to short chainpolymers which exhibit an affinity for the surface and which terminatein a moiety having an affinity for the suspension or dispersion medium.Such affinity improves the stability of the suspension and discouragesflocculation of the nanocrystallite.

The nanocrystallites can be suitable for a variety of applications,including those disclosed in copending and commonly owned U.S. patentapplication Ser. No. 09/156,863, filed Sep. 18, 1998, Ser. No.09/160,454, filed Sep. 24, 1998, Ser. No. 09/160,458, filed Sep. 24,1998, and Ser. No. 09/350,956, filed Jul. 9, 1999, all of which areincorporated herein by reference in their entirety. For example, thenanocrystallites can be used in optoelectronic devices includingelectroluminescent devices such as light emitting diodes (LEDs) oralternating current thin film electroluminescent devices (ACTFELDs).

EXAMPLES

Synthesis of Nanocrystallites

All reactions were done under a dry argon atmosphere. Tri-octylphosphineoxide (TOPO) was obtained from Strem. Tri-octylphosphine (TOP) wasobtained from Fluka, 1-hexadecylamine was obtained from Aldrich, andcadmium 2,4-pentanedionate (cadmium acetylacetonate, Cd(acac)₂) wasobtained from Alfa. Other starting materials were obtained from Aldrich.

A Cd precursor mixture was prepared by combining 8 mL (18 mmol) oftri-octyl phosphine (TOP), 427.4 mg (1.38 mmol) of Cd(acac)₂, and 792.6mg (3.07 mmol) of 1,2-hexadecanediol. The mixture was degassed at 100millitorr and purged with dry argon three times. The mixture was thenstirred at 100° C. for 90 minutes resulting in a waxy gel. The Cdprecursor was cooled to room temperature.

A 1M stock solution of trioctylphosphine selenide (TOPSe) was preparedby dissolving 0.1 mol of selenium shot in 100 mL of TOP under a dryargon atmosphere. 2 mL of one molar TOPSe in TOP were stirred into theCd precursor mixture and the combination of materials was loaded into asyringe under dry argon.

9.25 g (24 mmol) of tri-octylphosphine oxide (TOPO) and 5.75 g (24 mmol)of 1-hexadecylamine were dried and degassed at 160° C. and 60 millitorrfor two hours with stirring in a three-neck round-bottom flask. Theatmosphere of the flask was backfilled with dry argon at one atmosphereand the temperature of the molten reaction solvent was increased from160° C. to 360° C. The reaction mixture in the syringe was quicklyinjected into the stirring solvent, and the heat was temporarilyremoved. The temperature dropped to 265° C. Heat was then added toincrease the temperature to 275° C. for controlled growth of the CdSenanocrystallites.

Periodically, aliquots of the reaction solution were removed through aseptum via syringe and diluted in hexane for visible absorption spectralanalysis of the nanocrystallite growth. Once the target nanocrystallitesize was obtained, the temperature of the reaction solution was loweredto 100° C. and the growth solution was stirred overnight.

The synthetic procedure yielded CdSe nanocrystallites using cadmiumiodide, cadmium bromide, cadmium carbonate, cadmium acetate, or cadmiumhydroxide as the Cd-containing starting material. When cadmium metal wasused as the Cd-containing starting material, the Cd precursor materialwas prepared by combining the cadmium metal, TOP and 1,2-hexadecanedioluntil the metal dissolved. The precursor solution was then combined withthe TOPSe stock solution and was stirred for 12 hours at 100° C. Thissolution was then combined with the coordinating solvent to grow thenanocrystallites.

Absorption and Photoluminescence Spectra of Nanocrystallites

The absorption spectrum was taken with a Hewlett Packard Model 8453Ultraviolet-Visible (UV/Vis) Spectrometer. The emission spectrum wastaken with a SPEX 1680 0.22 m Double Spectrometer, using rhodamine 590in methanol as a quantum efficiency reference.

The average diameter of the CdSe nanocrystallites was estimated from theUV/Vis absorption spectrum to be roughly 38 Å after growth. Resolutionof the 1^(st), 2^(nd), and 3^(rd) features of the absorption spectrumindicates that the size distribution of the nanocrystallites wasrelatively narrow, less than 5% RMS deviation. The quantum efficiency ofthe CdSe nanocrystallite emission when irradiated with 500 nm light was10.25%±0.75%.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the methods and products described herein primarily related tomethods of preparing cadmium selenide or zinc sulfide materials.However, it will be apparent to those skilled in the art that thesemethods can be extended to other metal chalcogenide and pnictidematerials. Accordingly, other embodiments are within the scope of thefollowing claims.

1. A method of manufacturing a nanocrystal comprising heating a mixture including a coordinating solvent, a chalcogen or pnictide source, and a metal-containing compound to form a nanocrystal, wherein the metal-containing compound is free of metal-carbon bonds.
 2. The method of claim 1, wherein the mixture further comprises a primary amine.
 3. The method of claim 2, wherein the primary amine is a C₈-C₂₀ alkyl amine.
 4. The method of claim 1, wherein the mixture further comprises a 1,2-diol or an aldehyde.
 5. The method of claim 4, wherein the 1,2-diol is a C₆-C₂₀ alkyl diol or the aldehyde is a C₆-C₂₀ aldehyde.
 6. The method of claim 1, wherein the metal-containing compound includes a halide, carboxylate, carbonate, hydroxide, or diketonate.
 7. The method of claim 1, wherein the metal-containing compound includes a Group II metal or a Group III metal.
 8. The method of claim 1, wherein the metal-containing compound includes cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium hydroxide, cadmium carbonate, cadmium acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc hydroxide, zinc carbonate, zinc acetate, magnesium acetylacetonate, magnesium iodide, magnesium bromide, magnesium hydroxide, magnesium carbonate, magnesium acetate, mercury acetylacetonate, mercury iodide, mercury bromide, mercury hydroxide, mercury carbonate, mercury acetate, aluminum acetylacetonate, aluminum iodide, aluminum bromide, aluminum hydroxide, aluminum carbonate, aluminum acetate, gallium acetylacetonate, gallium iodide, gallium bromide, gallium hydroxide, gallium carbonate, gallium acetate, indium acetylacetonate, indium iodide, indium bromide, indium hydroxide, indium carbonate, indium acetate, thallium acetylacetonate, thallium iodide, thallium bromide, thallium hydroxide, thallium carbonate, or thallium acetate.
 9. The method of claim 1, wherein the mixture further comprises a C₈-C₂₀ alkyl primary amine, a C₆-C₂₀ alkyl 1,2-diol, and the metal-containing compound is a halide, carboxylate, carbonate, hydroxide, or diketonate.
 10. The method of claim 1, wherein the chalcogen or pnictide source includes a phosphine chalcogenide, a bis(silyl)chalcogenide, dioxygen, an ammonium salt, or a tris(silyl)pnictide.
 11. The method of claim 1, wherein the nanocrystal photoluminesces with a quantum efficiency of at least 10%.
 12. The method of claim 1, further comprising monitoring the size distribution of a population including of the nanocrystal.
 13. The method of claim 12, further altering the temperature of the mixture in response to a change in the size distribution.
 14. The method of claim 1, wherein the nanocrystal has a particle size in the range of about 20 Å to about 125 Å.
 15. The method of claim 1, wherein the nanocrystal includes ZnS, ZnSe, CdS, CdSe, or mixtures thereof.
 16. The method of claim 1, further comprising exposing the nanocrystal to an organic compound having affinity for a surface of the nanocrystal.
 17. The method of claim 1, further comprising forming an overcoating of a semiconductor material on a surface of the nanocrystal.
 18. The method of claim 1, wherein the nanocrystal is a member of a substantially monodisperse core population.
 19. The method of claim 18, wherein the population emits light in a spectral range of no greater than about 75 nm full width at half max (FWHM).
 20. The method of claim 18, wherein the population exhibits less than a 15% rms deviation in diameter of the nanocrystal.
 21. A method of manufacturing a nanocrystal, comprising: contacting a metal, M, or an M-containing salt, and a reducing agent to form an M-containing precursor, M being Cd, Zn, Mg, Hg, Al, Ga, In, or Tl; contacting the M-containing precursor with an X donor, X being O, S, Se, Te, N, P, As, or Sb to form a mixture; and heating the mixture to form the nanocrystal.
 22. The method of claim 21, wherein the reducing agent includes a 1,2-diol or an aldehyde and the M-containing salt includes a halide, carboxylate, carbonate, hydroxide, or diketonate.
 23. A method of manufacturing a nanocrystal, comprising: contacting a metal, M, or an M-containing salt, M being Cd, Zn, Mg, Hg, Al, Ga, In, or Tl, an amine, and an X donor, X being O, S, Se, Te, N, P, As, or Sb to form a mixture; and heating the mixture to form the nanocrystal.
 24. The method of claim 23, wherein the amine is a C₆-C₂₀ primary amine and the M-containing salt includes a halide, carboxylate, carbonate, hydroxide, or diketonate.
 25. A method of overcoating a core nanocrystal comprising: contacting a core nanocrystal population with an M-containing salt, M being Cd, Zn, Mg, Hg, Al, Ga, In, or Tl an X donor, X being O, S, Se, Te, N, P, As, or Sb, and an amine to form a mixture, and forming an overcoating having the formula MX on a surface of the core. 